In gasification plant reactors provided with outer walls formed of brickwork surrounded by a steel jacket, the brickwork is known to gradually erode as a result of the high temperatures at which the plants are operated. Unless at least a predetermined minimum thickness of the brickwork wall is maintained, the steel jacket of the reactor can be easily damaged or destroyed by overheating. As a consequence of the high sensitivity of the brickwork to temperatures that even slightly exceed permissible limits, fairly accurate measurements of the internal temperature of the reactor must be available; a maximum measurement error of 10.degree. C. is typically important.
In oil gasification plant reactors, which are operated at temperatures of 1,000.degree. to 1,700.degree. C., measurement of the internal operating temperature using conventional thermocouples presents no particular difficulty. Platinum-rhodium-platinum thermocouples enclosed in a gas-tight aluminum oxide tubular jacket and further surrounded by an outer protective tube of non-gas-tight aluminum oxide have been conventionally used in that environment without major problems.
However, in coal gasification plant reactors, which operate at temperatures of 1400.degree. C., these platinum-rhodium-platinum thermocouples have been found generally unsuitable for internal temperature measurement. Slag in the interior of the reactor tends to penetrate the protective tubes, lowering the melting point of the aluminum oxide and thereby impairing its effectiveness in sheathing the thermocouple. As a result, hydrogen and carbon monoxide come into corrosive contact with the thermocouple, at first causing false measurements and eventually destroying the thermocouple so that continued direct measurement of the internal reactor temperature becomes impossible. Like problems also occur when protective tubes formed of other ceramic materials or of high melting point metals are used.
Various alternate methods of measuring the internal operating temperature of a coal gasification reactor have been relied upon in the past. In some instances, direct temperature measurement has been passed up and the internal temperature has been indirectly measured by calculation from auxiliary operating parameters such as heat balances and gas compositions. Another "solution" has been to employ a covered thermocouple in which the normal stresses of high pressure and temperature are reduced by the use of thin, resistant ceramic protective walls, although this latter method often involves considerable measurement errors and substantial sluggishness in measurement response or reaction time for which appropriate correction factors must be estimated.
In any event, because the brickwork is so highly susceptible to considerable damage from even short term deviations from the elevated temperatures at which reactor operation is desired, employment of indirect methods for measuring internal reactor temperature presents considerable drawbacks. Direct temperature measurement is much preferred so that the accuracy of the remaining indirect measurement methods can be directly monitored on either a continuous basis or at regular, short term intervals.
It is therefore the desideratum of the present invention to provide a method and apparatus by which the internal temperature of a high temperature reactor can be directly measured over a substantial time period with a high degree of accuracy and without deterioration or destruction of the apparatus by the action of slag.
It is a further object of the invention to provide such an apparatus and method for temperature measurement which simultaneously monitors erosion of the brickwork.